1. Field of the Invention
This invention relates to a turbogenerator machine and more particularly to an improved device for detecting gas leakages which may occur in the cooling system of the machine.
2. Description of the Prior Art
Dynamoelectric machines used in the production of electrical power are typically cooled by a dual cooling system, as for example described by Y. S. Hargett, in a publication entitled, "Large Steam Turbine-Driven Generator", General Electric Company, Schenectady, N.Y., 1980. For many years, all of the larger turbine-generators have been designed to operate in a gas cooling system, e.g., hydrogen atmosphere, which is maintained in the gas-tight casing of the generator. The stator windings are also separately cooled through a liquid cooling system by flowing a liquid, preferably water, through the individual strands of the stator bars.
Conventionally, the gas within the casing of the machine is maintained at a higher pressure than the pressure of the water used to cool the stator windings. The pressure differential between the gas cooling system and the liquid cooling system makes it possible to detect leakage between them. Thus, should a leak occur, the gas is forced to enter the liquid cooling system from which samples may be withdrawn and analyzed. When such leakages become excessive, corrective action must be taken to avoid serious operating problems. It is therefore desirable to use a gas monitor and warning system to detect leakage of of the gas into the liquid cooling system.
An apparatus was described in Hungarian Patent No. 162,380 and in paper A78307-1 by I. K. Csillag, IEEE, PES Winter Meeting, January 1978, for automatically venting the water-cooled system of turbogenerator stator windings, continuously monitoring its gas tightness and providing a warning signal at a predetermined rate of gas penetration. The apparatus separates the unabsorbed gas from the liquid traversing it, and continuously measures the volume of the separated gas. After the accumulation of a predetermined volume of gas, the monitoring device automatically vents it. The number of ventings is recorded and a warning signal is provided at a predetermined rate of gas separation.
In the water-cooling system incorporating the Csillag apparatus, the gas bubbles are collected from the cooling water flow in a gas separator and continuously introduced with a portion of the cooling water into the apparatus. The gas is retained, while the cooling water portion flows further into an expansion chamber and from there continues into the main system of cooling water. The device also uses a specially designed U-tube which opens below the water level to vent the gas. Unfortunately this causes turbulence in the water and in high leakage situations may result in an obstructed gas path which may cause the device to stall.